The present invention relates to impact attenuators of the type now in widespread use to control the rate of deceleration of an errant vehicle as it approaches a hazardous fixed object in the highway environment. One of the more successful of these devices is disclosed in U.S. Pat. No. 3,606,258. That device, comprises an array of frangible containers or barrier modules each containing a dispersible mass, such as sand, which is located such that its center of gravity is elevated to that level which simulates the center of mass of the average vehicle.
The lower portion of the modules contain a lightweight core assembly and the upper portion is filled with the dispersible mass. In a typical case, the modules may have a diameter of approximately 36 inches and a height of approximately 36 inches. The weight of the modules, which may be varied to suit the requirements of a particular installation, ranges from some four hundred pounds to over two thousand pounds. The individual modules must have sufficient strength to retain the sand load without fracture or deformation and yet be sufficiently fragile so that on impact by a vehicle they will break up to permit dispersion of the sand without the formation of large relatively heavy pieces which would be hazardous to other persons or vehicles.
As disclosed in the '258 patent, and as actually manufactured, the individual modules are constructed in two identical halves, one edge of each half being formed with a flange overlapping the edge of the adjacent half, the parts being secured together by rivets. Typically twelve integrally molded holes are provided in each flange to accommodate the rivets. While this connection has adequate initial strength it is subject to premature failure resulting from stress concentration around the rivet holes.